CRETACEOUS PERIOD. 189 



while the rock of the other locaHty is soft, clayey shale, with thin intercalated 

 layers of impure limestone. 



Position and localiti/.— Strata of the Cretaceous period; plateau near the 

 west crossing of the North Fork of Virgin River, and elsewhere near the 

 North Fork of that river, Utah. 



Class GASTEROPODA. 



Subclass DICECA. 

 Order RlilPHIDOGLOSSA. 



SuBORDEK PODOPHTHALMA. 



Family NEEITIDiE. 



Genus NEEITIis^A Lamarck, 1809. 



Subgenus VELATELLA Meek, 1872. 



Neritina (Velatella) carditoides Meek. 



Plate XVIII, fig. 7 a, i, and c. 



Neritina (Bostia?) carditoides Meek, 1872, Geol. Surv. Montana, Idaho, Wyoming, and 

 Utah, 499. 



Shell of medium size, broadly oval in marginal outline, depressed-con- 

 vex; apex subspiral, slightly obliqiie, reaching nearly to the posterior margin, 

 and depressed nearly upon the posterior border; inner lip occupying a little 

 more than half the under surface of the shell, smooth, slightly convex, appar- 

 ently thick, but really' thinned by absorption within ; the free margin of the 

 inner lip somewhat sharp, straight, plain ; OLiter lip thickened, coarsely and 

 somewhat obscurely crenulate ; aperture subreniform, considerably less in 

 size than one-half the under surface of the shell. The space between the 

 shelf-like inner lip and the roof of the shell is partially divided by a thin, 

 slightly-twisted process or vertical partition, which extends inward and 

 backward from the antero-dextral corner directly toward, but not reaching, 

 the apex, so that communication between the two portions of the space thus 

 partially divided was around the posterior edge of the partition. 



Surface marked by fifteen or twenty radiating costse similar to those 

 that mark Cardium or Cardita, and these are crossed by numerous distinct 

 lines of growth. - 



